标题： 黑洞附近的零能旋转吸积流 显示英文标题

标题： Zero Energy Rotating Accretion Flows near a Black Hole

摘要： 我们通过比角动量来刻画接近黑洞的冷绝热气体薄的、轴对称的、无粘性的吸积流的性质。利用二维圆柱几何流体力学模拟，我们展示了吸积流表现出明显不同行为的各种状态。当流动具有较小的角动量 $(\lambda\lsim\lambda_b)$ 时，大部分物质被吸积到黑洞中，形成准球形流动或围绕它的简单盘状结构。当流动具有较大的角动量（通常大于边际结合值 $\lambda\gsim\lambda_{mb}$）时，几乎没有任何物质吸积到黑洞中。相反，流动在它后面产生一个稳定的驻波，可能伴随一个或多个涡旋，并且在激波处以高熵的锥形出流风的形式被偏转离开。如果流动的角动量略小于 $\lambda_{mb}$ $(\lambda_{u}\lsim\lambda\lsim\lambda_{mb})$，则有部分（通常是 \($5-10$\% \））的入射物质被吸积到黑洞中，但形成的流动结构与 $\lambda\gsim\lambda_{mb}$ 类似。一些被偏转的物质再次被吸积回黑洞，而其余部分则以出流风的形式吹走。 这两个与$\lambda\gsim\lambda_u$相关的情况对应于 Molteni、Lanzafame 和 Chakrabarti（1994）以及 Ryu\etal （1995）之前的研究工作。然而，发现角动量接近临界稳定值$(\lambda_{ms})$的流体是不稳定的。更具体地说，如果$\lambda_b\lsim\lambda\sim\lambda_{ms}\lsim\lambda_u$，流体显示出明显的周期性，这意味着盘的内部分不断形成。 显示英文摘要

摘要： We characterize the nature of thin, axisymmetric, inviscid, accretion flows of cold adiabatic gas with zero specific energy in the vicinity of a black hole by the specific angular momentum. Using two-dimensional hydrodynamic simulations in cylindrical geometry, we present various regimes in which the accretion flows behave distinctly differently. When the flow has a small angular momentum $(\lambda\lsim\lambda_b)$, most of the material is accreted into the black hole forming a quasi-spherical flow or a simple disk-like structure around it. When the flow has a large angular momentum (typically, larger than the marginally bound value, $\lambda\gsim\lambda_{mb}$), almost no accretion into the black hole occurs. Instead, the flow produces a stable standing shock with one or more vortices behind it and is deflected away at the shock as a conical outgoing wind of higher entropy. If the flow has an angular momentum somewhat smaller than $\lambda_{mb}$ $(\lambda_{u}\lsim\lambda\lsim\lambda_{mb})$, a fraction (typically, $5-10$\%) of the incoming material is accreted into the black hole, but the the flow structure formed is similar to that as for $\lambda\gsim\lambda_{mb}$. Some of the deflected material is accreted back into the black hole, while the rest is blown away as an outgoing wind. These two cases with $\lambda\gsim\lambda_u$ correspond those studied in the previous works by Molteni, Lanzafame, \& Chakrabarti (1994) and Ryu \etal (1995). However, the flow with an angular momentum close to the marginally stable value $(\lambda_{ms})$ is found to be unstable. More specifically, if $\lambda_b\lsim\lambda\sim\lambda_{ms}\lsim\lambda_u$, the flow displays a distinct periodicity in the sense that the inner part of the disk is built and